This invention relates to gas separation membranes from chemically and UV treated polymers of intrinsic microprosity and methods for making and using these membranes.
Membrane-based technologies have advantages of both low capital cost and high-energy efficiency compared to conventional separation methods. Several applications of membrane gas separation have achieved commercial success, including nitrogen enrichment from air, carbon dioxide removal from natural gas and from enhanced oil recovery, and also in hydrogen removal from nitrogen, methane, and argon in ammonia purge gas streams. For example, UOP's Separex™ cellulose acetate (CA) spiral wound polymeric membrane is currently an international market leader for carbon dioxide removal from natural gas. Polymers provide a range of properties including low cost, high permeability, good mechanical stability, and ease of processability that are important for gas separation. Glassy polymers have stiffer polymer backbones and therefore let smaller molecules such as hydrogen and helium pass through more quickly, while larger molecules such as hydrocarbons pass through more slowly as compared to polymers with less stiff backbones. CA glassy polymer membranes are used extensively in gas separation. Currently, CA and polyimide membranes produced by UOP are used for natural gas upgrading, including the removal of carbon dioxide. Although these membranes have many advantages, improvements would be desirable in several areas including selectivity, permeability, and in chemical, thermal, and mechanical stability. In addition, gas separation processes based on glassy polymer membranes frequently suffer from plasticization of the stiff polymer matrix by the sorbed penetrating molecules such as CO2 or C3H6. Plasticization of the polymer is exhibited by swelling of the membrane structure and by a significant increase in the permeances of all components in the feed and decrease of selectivity occurring above the plasticization pressure when the feed gas mixture contains condensable gases.
Polymers of intrinsic microporosity (PIMs) were originally reported by McKeown, et. al. These polymers have an extremely porous structure because of their spirocyclic backbone. Membranes formed from these polymers exhibit extremely high permeability for gases such as CO2, CH4, and propylene. However, these membranes made from polymers of intrinsic microporosity typically have low selectivity for gas separations, including CO2/CH4 separations. U.S. Pat. No. 7,758,751 taught that some membranes made from polymers of intrinsic microporosity that are subjected to UV light display much higher selectivity. Diazides have shown the ability to undergo chemical cross-linking with certain polymers when subjected to high temperatures. Most notably, Guiver, et. al. (Macromol. Rapid Commun. 2011, 32, 631) showed that diazides can react with PIM-1 to generate chemically cross-linked structures. However, no significant improvement in selectivity of these membranes for carbon dioxide/methane separation was observed with these chemical crosslinking reagents. A desirable membrane needs to have a combination of high permeability with high selectivity.
The present invention discloses a new type of chemically and UV treated polymer of intrinsic microporosity membrane and methods for making and using these membranes.